In the case of a V-bottomed boat, as speed increases, the supporting surface, which is the wetted surface, is known to become reduced thus lessening resistance to the boat""s forward movement.
The mass of water compressed by the moving boat is turned from its smooth state in directions orthogonal to its surface producing reactions opposing the motion, in practice constituting the lift of the boat.
Due to the boat""s motion, this mass tends to acquire a high degree of energy creating a considerable raising force.
The directions taken by this divided mass, in actual fact composed of compressed air and water, vary according to the flare of the bottom, to the trim and speed of the boat and to other factors.
It is known that by fitting longitudinal runners to the bottom, greater lift is obtained for the boat at its impact with the waves, not only forward impact but also that after the boat has left the surface of the water, for greater transversal and longitudinal stability as well as for higher speed since an increase in applied power progressively reduces surface friction.
With runners, however, speed can only be increased to a point depending both on the weight of the boat and on the power applied to it, as the water tends to escape sideways from the keel more easily.
The V-shaped bottom in particular is only partly satisfactory as beyond a certain limit the wetted or friction-creating surface cannot be reduced unless excessive power is applied which makes for uneconomic costs and consumption in relation to the performance achieved.
The above invention appreciably increases lift in relation to speed, greatly improving performance, strengthening the structure of the boat and offering other advantages as will now be explained.
Subject of the invention is a V-shaped bottom for fast motorboats, having in it a number of longitudinal means substantially parallel and symmetrical to the keel, with walls that react to the lateral thrust from the water-air mixture tending to move from the keel outwards to the sides of the bottom.
The walls of said means of reaction join the bottom in wide curves; they extend from the stern approximately as far as the bows, or else those nearest the keel can extend from a position midway between stern and the centre of the boat practially as far as the bows and, for the greater part of their length, the cross section will be of a constant shape.
The cross section of the means of reaction nearest the keel may be of a different shape from that of the means farthest from it.
There may be two, four or some other number of means of reaction.
In one type of execution the means of reaction consist of grooves.
The base of these grooves is substantially flat, their walls stand at substantially 90xc2x0 and are joined to the bottom in wide curves.
The curve is advantageously an arc of a circle with a radius equal to the height of the walls.
In one type of execution the grooves have a flat base and walls at 90xc2x0 with a wide curve on the wall nearest the keel, or on the wall farthest from said keel.
The rims of the grooves are preferably rounded.
In one advantageous type of execution, between one groove and the next the surface of the bottom lies at an angle outwards from the rim of a groove nearest to the keel, and in a direction opposite to the keel, which angle produces, in the adjacent groove farther from the keel, a wall height of said groove, nearer to the keel, higher than the opposite wall.
Cross section of the grooves may advantageously form an arc of a circle.
The reference U.S. Pat. No. 4,722,294 discloses longitudinal channels on the bottom of the keel of a hydroplane, these being symmetrical and parallel to the centre line of the keel, width as W, and having a substantially semicircular cross section of radius R open towards the outside, with width W established by the formula W=2R.
It follows that there can be no flat zone on the base of the keel between the opposite walls of said channels.
The purpose of these channels is to form a xe2x80x9cwater guidexe2x80x9d to increase stability of the boat avoiding side slippage and in particular a reduction of the tacking radius, but they cannot appreciably increase lift especially in relation to speed.
The return drop of the keel into the water after passing a wave that lifted it above the surface will even so be precipitate and produce shocks and bouncing.
In another type of execution the means of reaction are ribs, one effect of which is to strengthen the structure so as better to withstand thrust from the air-water mixture. Cross section of said ribs is substantially trapezoidal with a flat external lesser base substantially orthogonal to the boat""s longitudinal geometrical plane of symmetry.
Advantageously the sides of the ribs lie at an angle of substantially 45xc2x0 or of 90xc2x0 and join the surface of the bottom in a wide curve.
The edges of the ribs are bevelled.
The invention offers evident advantages.
The mass of water mixed with air, thrust by the keel towards the walls of the means of reaction, produces an important factor of lift partly due to the effect of the wide curves joining said walls to the outer surface of the bottom.
In particular the flow of water-air from bows to stern and the considable increase in its density determine a much higher lift especially in relation to the speed.
The particles of water slide more easily over the bottom because of the cushion of air mixed with water.
Especially in the case of means of reaction with strongly joined walls, in addition to greater containment of the mass of water supporting planing, the drop of the boat after the bottom rises above the water is made smoother and easier.
Water thrust is spread more evenly over a curved surface resulting in improved performance.
The pronounced curve at the join between the walls of the means of reaction and the bottom of the boat greatly improves structural strength and therefore higher resistance to stresses.